1. Field of the Invention
The present invention relates to a data transmission control device for controlling transmission of supervisory control data among a plurality of divided units in vehicles.
2. Description of the Prior Art
There have been required a large number of control signals to drive an automotive safely and comfortably, and individual signal buses formed by wire harnesses have been adopted heretofore for the transmission of these control signals.
However, since the wire harnesses differ from one another depending on the type of each vehicle and extremely numerous number of signal busses are required nowadays, there has been developed a control system wherein various supervisory control equipments and each unit respectively connected thereto are divided into a plurality of ranges in accordance with the location and function thereof, wherein signal data between the supervisory control equipments and each unit respectively connected thereto in each of the divided ranges are transmitted by way of individual signal busses, while signal data among each of the units in different ranges are transmitted by way of a multiple-signal data bus.
For example, there is disclosed a control system adopted in an automotive heretofore in FIG. 3, which system being divided into 8 different ranges respectively having different units; an engine unit 21, an instrument panel units 22, a console unit 23, a right and a left cowl units respectively 24 and 25, a right and a left door units respectively 28 and 27, and a trunk unit 28, wherein a data transmission among each of the units is performed by way of a multiple-signal data bus 10, and each unit is connected to supervisory control equipments in each of the divided ranges by way of individual signal busses. For example, a horn switch to make a horn sound is connected to the instrument panel unit 22, while a power switch to set on and/or off a power supply to make a horn sound is connected to the engine unit 21, wherein when the horn switch is set to on, the "on" signal is transmitted to the engine unit 21 to make a horn sound.
In FIG. 4, there is shown a frame structure of a signal for transmitting signal data among the different units, which frame being constructed by an SOF signal indicating that this is the first signal of the frame, a PRI signal indicating the priority of the data, a DADR signal showing a destination address to which the data is to be transmitted, a SADR signal showing a source address from which the data is sent, a CRC check signal for checking whether or not the transmitted data is correct, an EOD signal indicating the end of the data, a RES signal showing a response with respect to the transmitted data, and an EOF signal indicating the end of the frame. These signals are all represented by binary digits "1" or "0" and the signal "1" and "0" are distinguished from each other by a PWM (Pulse-width Modulation) as shown in FIG. 5, wherein with respect to one-bit length of a data, when an electric voltage is maintained for one-third of the one-bit length, it is defined as "1", whereas when an electric voltage is maintained for two-third of the one-bit length, it is defined as "0".
When a request for data transmission is generated, each of the units certifies that the multiple-signal data bus 10 is in an idle state, which means that there is no data transmission being performed between other units, and then sends data with a frame structure as described in FIG. 4 to the multiple-signal data bus 10.
Each of the units keeps detecting the signals being transmitted in the multiple-signal data bus 10, and when the DADR of the transmitted data coincides with the address number of the unit itself that has detected the signal, and if there is no error detected in accordance with the CRC check signal, then the unit sends back an ACK signal in the bit for RES signal, whereas the unit sends back a NAC signal if an error is detected. It should be noted that the unit sends back the address of itself as the ACK signal.
When the unit that has sent the data (hereinafter referred to just as a source unit) receives a NAC signal in the bit for RES signal from the unit that has sent back the NAC signal (hereinafter referred to just as a destination unit), the source unit sends the same data again until an ACK signal is sent back thereto from the destination unit. By the way, since the multiple-data signal bus 10 is commonly used by each of the units, there is an occasion that a plurality of units simultaneously send data to the multiple-signal data bus 10, and in such a case, an arbitration to decide which of the units can use the data bus 10 can be performed through a contention mode.
There is shown an example of the contention mode in FIG. 6, wherein when a "1" is sent from unit A, and "0" is sent from unit B simultaneously, then a signal selected by the multiple-signal data bus will be "0". Accordingly, each unit monitors the value of the signal in the multiple-signal data bus, and stops sending the signal therefrom when the signal that the unit has sent and the signal in the multiple-signal data bus do not coincide with each other. In the case shown in FIG. 6, unit A stops sending the data.
As mentioned heretofore, in the conventional data transmitting method between the units, when the data received by a destination unit has no error therein, an ACK signal is sent back therefrom to the source unit, whereas when an error is discovered in the received data, a NAC signal is sent back, wherein an arbitration for the multiple-signal data bus is decided by the contention mode.
However, there are also data which should be received by a plurality of supervisory control equipments. For example, there are equipments which should operate only when the engine is in operation, but stop the operation thereof in connection with a stoppage of the engine and cut electric power supply thereto from a battery. For transmitting the same data to a plurality of supervisory control equipments in different ranges, there is also a method for transmitting the same data simultaneously to a plurality of units other than a method for transmitting the data to each of these units differently one after another.
For example, it is easy to put a specified address signal in the bit for a destination address DADR to indicate that the data is a common data to a plurality of units and when the data with this specified address is transmitted, each of the units defines it as a data for itself and processes it therein.
However, since an arbitration for the multiple-signal data bus is made by a contention mode, even in the case that a data with a specified address in the DADR is transmitted, resending of the data is executed in accordance with a response signal of only a contended unit. In other words, if the unit which has received a data with an error therein loses the contention for the multiple-signal data bus, a resending of the data thereto cannot be done, and thus no correct data will be transmitted afterwards.